1. Field of the Invention
This invention relates to a spherical photoelectric sensor for detecting a presence and vice versa of an object by irradiating an infrared light.
2. Description of the Prior Art
According to a conventional photoelectric sensor, a convex lens is disposed in a circular opening which is formed on a front wall of a box-shaped casing, and a light emitting element such as a light emitting diode or a light receiving element such as a phototransistor is positioned on a focal point of the convex lens. A lighting drive circuit, a signal amplifying circuit, a motion indicating lamp, a variable resistor and other components are all fixed on an internal wall of the box-shaped casing and electrically interconnected to each other, so that those components do not hinder light transmission from the convex lens up to the photoelectric sensor. The box-shaped casing is a closed type one, in which an electric wire is connected to both an input terminal and an output terminal.
FIGS. 4A and 4B show views of such a conventional photoelectric sensor, in which symbol A is a so-called reflective type photoelectric sensor comprising a light transmitting lens 2, a light receiving lens 3, a light emitting element 5, a light receiving element 6 and other electronic parts (not illustrated). Those components are all disposed in place within a box-shaped casing 1. Fixed on a side of the box-shaped casing 1 is a bracket 4 for regulating an optical axis. Numerals 4a and 4b respectively are a screw for regulating an optical axis.
Infrared light emitted from the light emitting element 5 is directed to a reflective mirror 7 through the light transmitting lens 2 as shown in FIG. 4B, and then the light is reflected upon the reflective mirror 7 and received by the light receiving element 6 through the light receiving lens 3. When an optical path of rays of light formed between the photoelectric sensor A and the reflective mirror 7 is shaded by an object 8 to be detected, the light receiving volume in the light receiving element 6 is varied, thereby variation of the light receiving volume is output as electric signals by the light receiving element 6. Thus, whether or not the object 8 to be detected is present in a detecting area can be detected.
In recent years, the structure of the photoelectric sensor has become more compact and more small-sized to respond to user's requirements. However, there exist two problems which hinder production of a compact photoelectric sensor.
Firstly, an assembly efficiency of the photoelectric sensor becomes lower as the structure of the photoelectric sensor casing becomes smaller. More specifically, when installing various electronic components on an inner wall of the casing, it is required to carry out such assembly by inserting a driver, pincers, a soldering iron and other tools into the interior of the casing. Accordingly, as the structure of the photoelectric sensor becomes smaller, the assembly work becomes more cumbersome.
Secondly, since the convex lens is employed to collect lights, a considerably broader space, i.e. a conical space is required for collecting the light toward the photoelectric element positioned on a focal point of the convex lens.
In other words, in order to enhance the performance of the photoelectric sensor, it is desirable to enlarge the diameter of the convex lens and increase the amount of the light collected. Thus, a focal distance of the convex lens becomes longer, whereby the effect of any outer disturbing light becomes less. Therefore, a convex lens having a larger diameter and a longer focal distance, as well as a broader conical space is needed.
As discussed above, a desire to make more compact the photoelectric sensor device is inconsistent with the betterment of its optical performance.
Thirdly, as shown in FIG. 4B, an optical axis of the infrared light emitted from the light transmitting lens 2 does not conform to an optical axis of the infrared light received by the light receiving lens 3, so that light receiving accuracy is decreased. Fourthly, it is cumbersome to regulate such an optical axes. As clearly shown in FIG. 4B, the disadvantage is that a plurality of screw have to be regulated exactly and speedily.